1. Field of the Invention
The present invention relates to a keyless printing press including an ink feeder section consisting of an ink source roller, a transfer roller, a doctor roller, an anti-hysteresis doctor disposed on the circumferential surface of the doctor roller, and the like, and also provided with a wetting device. A keyless printing press refers to a printing press in which ink keys provided in a doctor of an ink source roller are omitted.
2. Description of the Prior Art
One example of the above-mentioned keyless printing press in the prior art is shown in FIG. 5. In this figure, ink b within an ink reservoir 1 associated with an ink feed port 17 is sent under pressure through a suction pipe 2 and a delivery pipe 4 to an ink delivery nozzle 5 by means of a pump 3. The ink delivery nozzle 5 is disposed in opposition to and in parallel with the circumferential surface of the ink source roller 7 with a minute gap defined therebetween. The ink delivery nozzle 5 is provided with a large number of delivery holes aligned in the axial direction of the ink source roller 7. The ink delivered from the ink delivery nozzle 5 and adhered to the ink source roller 7 rotates jointly with the ink source roller 7 rotating at a low speed, and is metered into a predetermined thickness by passing through the minute gap defined between the ink source roller 7 and an ink feed doctor 6 disposed in parallel to the former. Surplus ink b.sub.1 is returned by the ink feed doctor 6 to the ink reservoir 1, while the ink having passed through the minute gap is transferred to a transfer roller 8 rotating at a high speed in contact with the ink source roller 7. Then, the transferred ink is fed to a plate drum 14 by the intermediary of a doctor roller 9 having an ink film of uniform thickness formed thereon by an anti-hysteresis doctor 10, and ink application rollers 11 and 12.
On the other hand, wetting water c is fed from a wetting device 13 to the plate drum 14. Thus, on the plate drum 14, ink adheres to a pattern portion while wetting water c adheres to a non-pattern portion, whereby a predetermined ink film image is formed. This ink film image is transferred via a blanket drum 15 to a paper sheet a.
In the above-described keyless printing press in the prior art, since ink b.sub.2 adhered to the doctor roller 9 and containing the wetting water c is scraped by the anti-hysteresis doctor 10 and is made to drop into the ink reservoir 1, the ink b delivered from the ink delivery nozzle 5 to the ink source roller 7 and adhering thereto contains 10-30% of wetting water c, and also, a part of the wetting water c flows inversely to the ink source roller 7 via the doctor roller 9 and the transfer roller 8.
Moreover, the proportion of water in the ink film transferred from the ink source roller 7 rotating at a low speed to the transfer roller 8 rotating at a high speed is unstable. And, in the case where the moisture content proportion of ink is high, the proportion of water is uneven along the width of the roller. Hence, the moisture content of residual ink on the ink source roller after passing through a nip between the ink source roller 7 and the transfer roller 8 is also uneven along the width of the ink source roller 7. Thus even if fresh ink having a uniform moisture content were fed into the residual ink, the unevenness of the moisture content of the ink film on the ink source roller 7 would be mitigated only a little, but the moisture content cannot be uniform. Accordingly, there exists a problem in that a difference arises in the proportion of ink or the amount of ink along the width of the roller, resulting in an uneven printing depth along the width of the roller.